# Maximum temperature - Opposite of absolute zero

## Recommended Posts

Sorcerer    33

I assume the hottest temperature the universe has ever contained was at the moment of the big bang. Is this possible to achieve again or beat in the current universe or would it be prevented by entropy?

What is our best estimate of the hottest possible temperature?

##### Share on other sites

I don't think there's any limit to highest temperature. It's because temperature is the measure of the average kinetic energy of the molecules contained in a body. This leads to the conclusion that temperature depends upon the supply of heat energy. So, if heat is withdrawn the intermolecular space decreases, thereby decreasing the space available for molecules to move, hence a decrease in kinetic energy. So temperature decreases. But there is a limit to the lowest temperature as at some point there will be no space to move. But, if you supply unlimited heat energy to the molecules, there will be an infinite space and a large kinetic energy. So the temperature shall increase unbounded.

##### Share on other sites
Sorcerer    33

I Googled and looked at the wiki, it's called "absolute hot" apparently. There's 3 main definitions there.

1. The Planck temperature, which has the value 1.416785(71)×1032 kelvin. (Which is what I was getting at I think) and is at a limit due to no theory of quantum gravity apparently.

2. The Hagedorn temperature. Where particle pair formation draws heat away from the area being heated, limiting it. As I understood it.

3."Quantum physics formally assumes infinitely positive or negative temperatures in descriptions of spin system undergoing population inversion from the ground state to a higher energy state by excitation with electromagnetic radiation. The temperature function in these systems exhibits a singularity, meaning the temperature tends to positive infinity, before discontinuously switching to negative infinity.[6] However, this applies only to specific degrees of freedom in the system, while others would have normal temperature dependency. If equipartitioning were possible, such formalisms ignore the fact that the spin system would be destroyed by the decomposition of ordinary matter before infinite temperature could be reached uniformly in the sample.[citation needed]"

Could someone clarify #3 for me please?

##### Share on other sites
swansont    6167

Could someone clarify #3 for me please?

In looking at excitations, you can measure temperature by looking at the distribution of populations in the excited states. That's fine for steady-state systems. A population inversion (more excited state atoms than ground state, or some other lower-energy state), which is not steady-state, yields a negative temperature. As you are changing the population distribution, you pass through infinite temperature. But it's because the assumption that you be in steady-state (or close to it) is being ignored. If you measured the KE distribution of the system, it would give a different (and reasonable) answer.

##### Share on other sites
Sorcerer    33

In looking at excitations, you can measure temperature by looking at the distribution of populations in the excited states. That's fine for steady-state systems. A population inversion (more excited state atoms than ground state, or some other lower-energy state), which is not steady-state, yields a negative temperature. As you are changing the population distribution, you pass through infinite temperature. But it's because the assumption that you be in steady-state (or close to it) is being ignored. If you measured the KE distribution of the system, it would give a different (and reasonable) answer.

How does this effect the practical limitations of us generating the maximum possible temperature? (As I see it #2 was the current limiting factor).

Are we in steady state or close to it? (What's steady state)?

What's the maximun KE?

How is spin involved?

Why does a population inversion give a negative temperature? (Doesn't that make you question the validity of the theory(asked without me understanding "steady state")?

Edited by Sorcerer

##### Share on other sites
swansont    6167

How does this effect the practical limitations of us generating the maximum possible temperature? (As I see it #2 was the current limiting factor).

Are we in steady state or close to it? (What's steady state)?

What's the maximun KE?

It doesn't affect the practical limitations. It means you aren't really measuring the temperature when you do it that way, under those conditions.

Steady state means the state of the system is not changing.

##### Share on other sites
Sorcerer    33

When is the state of a system not changing in regards to the system being defined as the universe?

I had to Google "For thermodynamics, a thermodynamic state of a system is its condition at a specific time, that is fully identified by values of a suitable set of parameters known as state variables, state parameters or thermodynamic variables."

Is anything actually in a steady state for more duration than our measuring tool?

Can there be the same system conditions with different variable values? If so how could we differentiate between steady state and not?

Edited by Sorcerer
• 1

##### Share on other sites

If the entropy is zero, the system must be in steady state (I think so).

##### Share on other sites
swansont    6167

The universe isn't steady-state; you can't assign a temperature to it. Stars are very hot, planets can be cold, and the CMB very cold.

• 1

##### Share on other sites
Strange    2431

I Googled and looked at the wiki, it's called "absolute hot" apparently. There's 3 main definitions there.

1. The Planck temperature, which has the value 1.416785(71)×1032 kelvin. (Which is what I was getting at I think) and is at a limit due to no theory of quantum gravity apparently.

That is only a limit in the sense that we don't have any theories that can describe what happens. It doesn't mean that there cannot be a higher temperature.

##### Share on other sites
J.C.MacSwell    172

There must be a steady state temperature for, say, a gas ball that would be a maximum. Particles would have the maximum kinetic energy without escape velocity from the ball, yet the gas ball would have to be limited in size and density such that it would not become a black hole.

Or is there something wrong with that assumption?